$C.N.G$ is........

Which of the following shows only one monobrominated compound upon reaction with $Br_2$ in the presence of light?

Identify $D$ and $E$ in the following reaction: $CH_3-CH(CH_3)-CH(CH_3)-CH_3 \xleftarrow[ether]{Na} R'-Br$ $\xrightarrow{Mg} D$ $\xrightarrow{H_2O} E$

Different hydrogen atoms in the compound are represented by alphabets:
$CH_3(A)-CH=CH(B)-CH_2(C)-CH_2(D)-CH(E)(CH_3)_2(F)$
Arrange them in decreasing order of reactivity towards free radical substitution.

As the number of carbon atoms in a chain increases,the boiling point of alkanes:

$A$ compound $A$ contains $C$ and $H$ only and has a molecular mass of $72$. Its photochlorination gives a mixture containing only one monochloro and two dichloro hydrocarbons. What is its $IUPAC$ name?